The explosive growth in wireless services over the past several years illustrates the huge and growing demand of the business community, consumers and the government for spectrum-based communications. Continuing advancements in technology, products and services are overwhelming the finite resources of the available communication spectrum. Industry has been forced to address dramatic changes, as it must adapt to accommodate the exponential demand on spectrum access, efficiency and reliability.
The Federal Communications Commission in the United States, and its counterparts around the world, allocate the radio spectrum across frequency channels of varying widths. One band can cover AM radio, another VH television, still others cell phones, citizen's-band radio, pagers, and so on. As more devices go wireless, they have to share a finite—and increasingly crowded—amount of radio spectrum. Although the radio spectrum is almost entirely occupied, not all devices use portions of the radio spectrum at the same time or location. At some locations or at some times of the day, a large percentage of the allocated spectrum may be sitting idle, even though it is officially accounted for.
Cognitive radio is a paradigm for wireless communication in which either a network or a wireless device changes its transmission or reception parameters to avoid interference with licensed or unlicensed users. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency usage, user behavior and network state. Although cognitive radios implement measures to avoid selecting an occupied frequency, there are times in which they may accidentally or unintentionally interfere with an incumbent device—a device authorized to use those frequencies of the radio spectrum. This can damage the incumbent device and/or reduce its signal reception quality. A need therefore exists to protect the incumbent devices from interference generated by the cognitive radios.